The Erythrocyte Sedimentation Rate (ESR) test, often called a sed rate, detects inflammation in the body. This measurement is a non-specific indicator, signaling that a disease process is occurring without identifying the specific cause. Healthcare providers use the ESR alongside a patient’s medical history, physical examination, and other diagnostic tools. Since inflammation is a defense response to conditions like infection, injury, or chronic disease, the sed rate serves as an initial screening tool.
Understanding the Erythrocyte Sedimentation Rate (ESR)
The ESR test quantifies the rate at which red blood cells settle to the bottom of a vertical tube of blood over a defined period, typically one hour. While gravity governs this settling process, the speed is influenced by certain plasma proteins. The Westergren method, the most common technique, measures the distance the red blood cells fall in millimeters per hour (mm/hr).
In a healthy state, red blood cells resist clumping and settle slowly due to their negative surface charge. When inflammation is present, the body produces increased acute-phase proteins, such as fibrinogen and immunoglobulins. These proteins coat the red blood cells, neutralizing their negative charge and causing them to stick together in stacks called rouleaux.
The formation of these larger, denser rouleaux aggregates increases the mass of the particles, causing them to fall more quickly through the plasma. A faster sedimentation rate, or a higher ESR value, indicates a higher level of systemic inflammation. The Westergren method uses an anticoagulated blood sample placed in a long, thin tube for measurement.
Establishing Normal Reference Ranges by Age
The normal range for the sed rate is not a single number but varies based on a person’s age and sex. Physiological differences mean an ESR value normal for an older adult might be elevated for a young child. The sedimentation rate naturally increases as a person ages, even without disease.
Reference ranges are divided by gender and age group, with all values reported in millimeters per hour (mm/hr). For children, the normal rate is lower; newborns often show rates between 0 and 2 mm/hr. Children up to puberty generally have a rate of 10 mm/hr or lower, with 0 to 20 mm/hr considered normal for children between the ages of two and puberty.
For adult males under 50, the upper limit is typically 15 mm/hr, increasing to 20 mm/hr for men over 50. Adult females generally have slightly higher baseline ESR values than males, often due to factors like menstruation and pregnancy. For women under 50, the normal upper limit is around 20 mm/hr, increasing to 30 mm/hr for women over 50.
This age-related increase occurs because aging is associated with minor increases in certain plasma proteins, which enhances rouleaux formation over time. Formulas exist to estimate the upper limit of a normal ESR based on age, such as dividing the age by two for men, or adding ten to the age and dividing by two for women. These age-adjusted ranges emphasize that a higher ESR value in an older, healthy person is often a normal physiological change, not a sign of disease.
Interpreting Deviations from the Norm
When the ESR falls outside the established reference ranges, it suggests an alteration in the plasma protein balance, prompting further medical evaluation. An elevated ESR, known as a high sed rate, is the most common deviation and signals increased inflammatory activity. Infections are a frequent cause, including osteomyelitis, endocarditis, or chronic infections such as tuberculosis.
A high ESR is also seen in autoimmune and inflammatory disorders, such as rheumatoid arthritis, systemic lupus erythematosus (lupus), and giant cell arteritis. Extreme elevations, often exceeding 100 mm/hr, suggest serious underlying conditions, including malignancies like multiple myeloma or chronic infections. However, a high ESR remains a non-specific finding and requires correlation with other clinical data and tests, such as C-reactive protein (CRP), to pinpoint the cause.
Conversely, a low ESR is a less common finding but can be clinically significant. A low rate means the red blood cells are resisting aggregation and settling slowly. This can be caused by conditions that affect the red blood cells’ shape, such as sickle cell anemia, which impairs rouleaux formation.
A low ESR may also be seen in polycythemia, a disorder characterized by an excess of red blood cells that increases blood viscosity and slows sedimentation. Technical factors can also alter the rate; for instance, a delayed blood sample or a tilted tube can lead to inaccurate readings. Interpretation of any sed rate result must consider the patient’s entire clinical picture and potential pre-analytical variables.